1. FIELD OF THE INVENTION
The present invention relates generally to hydraulic mount assemblies for vibration damping, and in particular, is concerned with a one-piece partition having a peripheral, resilient flange for use inside a hydraulic engine mount assembly.
2. DESCRIPTION OF THE RELATED ART
A variety of mount assemblies are presently available to isolate vehicle vibrations, such as for automobile and truck engines and transmissions. A popular mount is the hydraulic mount of the type disclosed in U.S. Pat. No. 4,588,173 to Gold et al., issued May 13, 1986, titled "Hydraulic-Elastomeric Mount" and assigned to the assignee of the present invention.
The hydraulic mount assembly of U.S. Pat. No. 4,588,173 includes a reinforced, hollow rubber body that is closed by a resilient diaphragm so as to form a cavity. This cavity is partitioned by an assembly of upper and lower plates into two chambers that are in fluid communication through a relatively large central opening in the plate assembly. A first or primary fluid chamber is formed between the plate assembly and the body. A secondary chamber is formed between the plate assembly and the diaphragm.
A decoupler is positioned in the central opening of the plate assembly and reciprocates in response to the vibrations. The decoupler movement alone accommodates small volume changes in the two chambers. For example, when the decoupler moves in a direction toward the diaphragm, the volume of the portion of the decoupler cavity in the primary chamber increases and the volume of the portion in the secondary chamber correspondingly decreases, and vice-versa. In this manner, fluid flow between the chambers is substantially avoided for certain small vibratory amplitudes that generally occur at higher frequencies. Thus, the freely floating decoupler is a passive tuning device.
In addition to the relatively large central opening, an orifice track with a smaller, restricted flow passage is provided around the perimeter of the plate assembly. Each end of the track has an opening. An inlet opening communicates with the primary chamber, while an outlet opening communicates with the secondary chamber. The orifice track provides a second passive tuning component, and when combined with the decoupler, provides at least three distinct dynamic operating modes. The particular operating mode is primarily determined by the flow of fluid between the two chambers.
More specifically, small amplitude vibrating input, such as from relatively smooth engine idling or the like, produces no damping due to the action of the decoupler, as explained above. Large amplitude vibrating input, such as heavy engine loading during sudden accelerations or panic stops, produces high velocity fluid flow through the orifice track, and accordingly, a high level of damping force and desirable smoothing actions. A third or intermediate operations mode of the mount assembly occurs during medium amplitude inputs experienced in normal driving and resulting in lower velocity fluid flow through the orifice track. In response to the decoupler switching from movement in one direction to another in each of the modes, a limited amount of fluid can bypass the orifice track by moving round the edges of the decoupler and through the central opening, thereby smoothing the transition.
While this basic mount design has proved successful, the art continues to seek improvements. It is desirable to reduce the weight of a mount assembly and the costs associated with tooling, material handling and assembly of the mount components.